A team of astronomers have captured the first images of a nova’s early fireball stage.
Supernovae may get all the spotlight in pop culture, but novae are still “truly remarkable celestial phenomena,” according to Professor Peter Tuthill of the University of Sydney’s Institute for Astronomy. When the gravity of a white dwarf star strips away matter from a nearby companion star, pressure builds up on the white dwarf until a thermonuclear explosion is triggered – a nova.
“Like a little stellar mosquito, the white dwarf continually sucks hydrogen from its partner, forming an ocean on its surface. After drawing about as much mass as the entire planet Saturn, the pressure reaches a critical point, then boom!” Tuthill explained.
“The stellar surface turns into one titanic hydrogen bomb hurling a fireball out into space and propelling a formerly dim, obscure star system into prominence as a nova in our night skies.”
As powerful and spectacular as the explosion is – and, in the case of the nova eruption that was seen on August 14, 2013, it was bright enough to be seen by the naked eye – it still takes some advanced equipment to capture it.
“The technical challenge posed requires magnification equivalent to watching a flower in my Spanish hometown of Algeciras unfold from here in Sydney, a distance of 12,000 kilometres away,” said Dr. Vicente Maestro of the University of Sydney.
Within hours of witnessing nova erupting on August 2013, astronomers were pointing California’s CHARA array at its expanding fireball. By combining light from six optical telescopes, the array is able to create very high resolution images, and the first readings it produced showed that the fireball was already as big as Earth’s orbit around the Sun. The last measurement was taken 43 days after the explosion, by which time the fireball had expanded nearly 20-fold – out to the equivalent of Neptune’s orbit. The results of the study were published in Nature.
“Bright novae go off every few years, but this is the first to have occurred in good weather since the development of reliable optical telescope interferometers,” said one of the study’s authors, Dr. Michael Ireland of the Australian National University. “Everything has come together to give us a really good look at one.”
The study found that the initial shape of the fireball was elliptical rather than spherical, and the manner in which the nova explodes in multiple shells was of interest to the astronomers.
“These new data allow us to study in detail exactly how the fireball evolves as the gas expands and cools. It seems like the ride is a lot more complicated and bumpy for the gas than the simple models used previously would have predicted,” said Dr. Theo ten Brummelaar of Georgia State University.
Next, the researchers would like to study the nova’s shock waves.